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Subclavian Steal Following Left Subclavian Artery Occlusion During Thoracic Endovascular Aortic Repair: Doppler Findings and Literature Review Thoracic endovascular aortic repair is the treatment of choice for numerous aortic conditions, including many traumatic thoracic aortic lesions, aneurysms, and acute and chronic dissections. The segments of the normal aorta proximal and distal to abnormalities are referred to as the “landing zones,” where a stent-graft is anchored. Traditionally, the proximal landing zone must be at least 15 mm in length to obtain an adequate seal for the stent. The proximity of many thoracic aortic abnormalities to the origin of the left subclavian artery necessitates that a stent-graft is often intentionally deployed across the left subclavian artery origin. Although antegrade flow around the stent-graft often minimally supplies the left subclavian artery immediately after occlusion, this flow typically does not persist.1 Occlusion of the left subclavian artery can compromise circulation to the left arm and potentially to the vertebrobasilar system. In a complete subclavian steal, the arterial supply to the arm is via blood flowing exclusively in a retrograde direction down the vertebral artery at the expense of the vertebrobasilar circulation. In an incomplete steal, vertebral artery flow may be biphasic, or flow reversal may be induced by exercise.2 Doppler findings of a subclavian steal have been extensively described.2,3 However, to our knowledge, a sub-
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clavian steal following intentional occlusion of the left subclavian artery has not been described in the ultrasound literature, nor have the Doppler findings of this common iatrogenic cause been illustrated. When the left subclavian artery origin is covered during thoracic endovascular aortic repair, circulation to the arm and vertebrobasilar system can be maintained by revascularization, typically either by transposition of the left subclavian artery to the left carotid or by a left carotid-to-left subclavian artery bypass. The need for revascularization is controversial and has been the subject of numerous vascular surgery studies.4–10 We observed the following sonographic findings in a patient who underwent thoracic endovascular aortic repair with intentional occlusion of the left subclavian artery. A 30-year-old man was brought to our center after a motorcycle collision and fall of approximately 100 ft. Initial imaging showed multiorgan system trauma, including traumatic aortic injury with a pseudoaneurysm of the distal aortic arch. He also had hepatic and splenic lacerations, extremity and pelvic fractures, and intracranial hemorrhage. The patient underwent exploratory laparotomy with packing of the abdomen for active bleeding of the liver. Two days after admission, the vascular surgery service performed thoracic endovascular aortic repair, with intentional occlusion of the left subclavian artery due to the location of the pseudoaneurysm. He also underwent reduction of multiple extremity fractures, with the exception of a left distal radius fracture. Minimal antegrade flow was seen in the occluded left subclavian artery on angiography immediately after thoracic endovascular aortic repair (Figure 1A). One week after aortic repair, the patient underwent a carotid duplex study as part of routine follow-up. The study showed flow reversal in the left vertebral artery, consistent with a complete subclavian steal (Figure 1B). The left subclavian artery was also abnormal, showing a monophasic, low-resistance waveform (Figure 1C). The right subclavian artery showed a normal triphasic waveform and highresistance flow. The patient’s mental status was still altered at this time, and although symptoms of the subclavian steal could not be accurately assessed, spontaneous left upper extremity movements were noted. Due to both the subclavian steal documented on sonography and the concomitant left radius fracture, the patient was taken for an uncomplicated left subclavian artery-to-left carotid artery transposition. Carotid duplex sonography 2 weeks later showed biphasic waveforms in the left vertebral artery (Figure 1D), as opposed to complete vertebral artery reversal preoperatively. This duplex study also showed normal high-
J Ultrasound Med 2015; 34:925–929
resistance systolic waveforms in the left subclavian artery, as opposed to low-resistance waveforms preoperatively. The findings were consistent with conversion of a complete subclavian steal to an incomplete steal after revascularization. The patient was extubated, with improving mental status soon after. Several early and smaller studies in the vascular surgery literature described good outcomes following left subclavian artery occlusion without prophylactic revascularization. Hausegger et al4 described 4 patients who required left subclavian artery occlusion during thoracic endovascular aortic repair. Although no neurologic complications or left arm ischemia were observed, the authors did note that left arm systolic blood pressures were lower than those of the right arm. Görich et al5 described 23 patients who required left subclavian artery coverage during thoracic endovascular aortic repair. Symptoms of left arm ischemia were described in 2 patients (exercise-related left hand paresthesias and a cool left hand). However, both patients refused revascularization due to spontaneous symptomatic improvement. The authors concluded that left subclavian artery coverage is generally well tolerated. Rehders et al6 reported 22 patients who required complete coverage of the left subclavian artery during thoracic endovascular aortic repair. There were no serious morbidities at a mean 2-year follow-up, although the mean differential systolic blood pressure in the left arm was 26% lower than in the right arm. Mild symptoms of a subclavian steal in 7 patients included exercise-induced weakness in 3, a mild sensation of left arm coolness in 3, and left arm paresthesias in 1. The authors challenged the need for prophylactic revascularization. Numerous other studies have reported higher complication rates for left subclavian artery occlusion without revascularization. Tiesenhausen et al7 performed thoracic endovascular aortic repair necessitating left subclavian artery occlusion in 10 patients, the first 2 of whom underwent prophylactic left subclavian artery-to-left carotid artery transposition. The remaining 8 patients were managed expectantly. Three of these 8 patients required left subclavian artery revascularization for subclavian steal syndrome with vertigo and left arm claudication. The authors concluded that prophylactic revascularization should be performed in patients with severe disease of the vertebral or internal carotid arteries. Riesenman et al8 performed thoracic endovascular aortic repair on 112 patients, a subset requiring complete (18 patients) or partial (10 patients) left subclavian artery coverage. Subclavian steal symptoms developed in 3 patients
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with complete left subclavian artery coverage, but none had symptoms severe enough to warrant intervention. Left arm rest pain developed in 1 patient with partial left subclavian artery coverage and was successfully treated by deployment of a left subclavian artery stent.
Figure 1. Complete subclavian steal following left subclavian artery occlusion during thoracic endovascular aortic repair, converted to an incomplete steal following left subclavian artery revascularization. A, Thoracic endovascular aortic stent-graft occluding the origin of the left subclavian artery (arrow). Blood flow in the thoracic aorta around the graft, often seen just after stent placement, is responsible for the minimal residual flow in the left subclavian artery. B, Initial Doppler examination showing reversal of flow in the left vertebral artery, consistent with a complete subclavian steal after left subclavian artery occlusion by a stent-graft. C, Initial Doppler examination showing an abnormal lowvelocity, low-resistance, monophasic waveform in the left subclavian artery after occlusion by the stent-graft. The left subclavian artery waveform normalized after revascularization (not shown). D, Doppler examination following revascularization (left subclavian artery-to-left carotid artery transposition) showing a biphasic left vertebral artery waveform, now consistent with an incomplete subclavian steal.
B
C
A
D
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In recent years, several meta-analyses and reviews have also examined the need for prophylactic revascularization of the left subclavian artery before occlusion. Rizvi et al9 compiled a meta-analysis of 51 observational studies and concluded that very low-quality evidence suggests that left subclavian artery coverage increases the risk of arm ischemia, vertebrobasilar ischemia, and possibly spinal cord ischemia and anterior circulation stroke. There were no significant associations between left subclavian artery coverage and death, myocardial infarction, or transient ischemic attacks. A review by Weigang et al10 concluded that only in acutely unstable patients is left subclavian artery coverage without prophylactic revascularization justified. Prophylactic revascularization of the left subclavian artery before coverage was deemed necessary in the setting of a dominant left vertebral artery, anomalous subclavian or vertebral arteries (such as a direct aortic arch origin of the left vertebral), functional compromise of the posterior circulation, and a prior coronary artery bypass graft using the left internal mammary artery. Left subclavian artery coverage without revascularization in any of these conditions could compromise the left arm or posterior circulation collateral blood supply. To our knowledge, the Doppler findings of a complete subclavian steal resulting from intentional left subclavian artery occlusion during thoracic endovascular aortic repair have not been reported previously. We also document improvement in the steal phenomenon, with conversion to an incomplete steal (biphasic waveforms) in the left vertebral artery after revascularization. With the increasing use of thoracic endovascular aortic repair with left subclavian artery occlusion for treatment of thoracic aortic disorders, this iatrogenic etiology of a subclavian steal may be observed more frequently in the future. Practitioners performing cerebrovascular sonography should be aware of this phenomenon. Doppler evaluation can play a part in preoperative evaluation of the carotid and vertebral circulation to identify candidates for prophylactic revascularization. In patients undergoing emergent thoracic endovascular aortic repair with left subclavian artery occlusion, preoperative Doppler imaging or revascularization may not be feasible. In these cases, Doppler documentation of the presence and severity (complete versus incomplete) of a subclavian steal following thoracic endovascular aortic repair may contribute to the decision to revascularize the left subclavian artery.
doi:10.7863/ultra.34.5.926
References 1.
Hausegger KA, Oberwalder P, Tiesenhausen K, et al. Intentional left subclavian artery occlusion by thoracic aortic stent-grafts without surgical transposition. J Endovasc Ther 2001; 8:472–476. 2. icenzini E, Ricciardi MC, Sirimarco G, Di Piero V, Lenzi GL. Extracranial and intracranial sonographic findings in vertebral artery diseases. J Ultrasound Med 2010; 29:1811–1823. 3. Ginat DT, Bhatt S, Sidhu R, Dogra V. Carotid and vertebral artery Doppler ultrasound waveforms: a pictorial review. Ultrasound Q 2011; 27:81–85. 4. Hausegger KA, Tiesenhausen K, Schedlbauer P, Oberwalder P, Tauss J, Rigler B. Treatment of acute aortic type B dissection with stent-grafts. Cardiovasc Intervent Radiol 2001; 24:306–312. 5. Görich J, Asquan Y, Seifarth H, et al. Initial experience with intentional stent-graft coverage of the subclavian artery during endovascular thoracic aortic repairs. J Endovasc Ther 2002; 9(suppl 2):II39–II43. 6. Rehders TC, Petzsch M, Ince H, et al. Intentional occlusion of the left subclavian artery during stent-graft implantation in the thoracic aorta: risk and relevance. J Endovasc Ther 2004; 11:659–666. 7. Tiesenhausen K, Hausegger KA, Oberwalder P, et al. Left subclavian artery management in endovascular repair of thoracic aortic aneurysms and aortic dissections. J Card Surg 2003; 18:429–435. 8. Riesenman PJ, Farber MA, Mendes RR, Marston WA, Fulton JJ, Keagy BA. Coverage of the left subclavian artery during thoracic endovascular aortic repair. J Vasc Surg 2007; 45:90–95. 9. Rizvi AZ, Murad MH, Fairman RM, Erwin PJ, Montori VM. The effect of left subclavian artery coverage on morbidity and mortality in patients undergoing endovascular thoracic aortic interventions: a systematic review and meta-analysis. J Vasc Surg 2009; 50:1159–1169. 10. Weigang E, Parker JA, Czerny M, et al. Should intentional endovascular stent-graft coverage of the left subclavian artery be preceded by prophylactic revascularisation? Eur J Cardiothorac Surg 2011; 40:858–868.
Mittul Gulati, MD, Nasim Khadem, MD, Ilya Lekht, MD, Hisham Tchelepi, MD, Edward G. Grant, MD Department of Radiology University of Southern California Keck School of Medicine Los Angeles, California USA J Ultrasound Med 2015; 34:925–929
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Clinical Letters
Subclavian Steal Following Left Subclavian Artery Occlusion During Thoracic Endovascular Aortic Repair: Doppler Findings and Literature Review Thoracic endovascular aortic repair is the treatment of choice for numerous aortic conditions, including many traumatic thoracic aortic lesions, aneurysms, and acute and chronic dissections. The segments of the normal aorta proximal and distal to abnormalities are referred to as the “landing zones,” where a stent-graft is anchored. Traditionally, the proximal landing zone must be at least 15 mm in length to obtain an adequate seal for the stent. The proximity of many thoracic aortic abnormalities to the origin of the left subclavian artery necessitates that a stent-graft is often intentionally deployed across the left subclavian artery origin. Although antegrade flow around the stent-graft often minimally supplies the left subclavian artery immediately after occlusion, this flow typically does not persist.1 Occlusion of the left subclavian artery can compromise circulation to the left arm and potentially to the vertebrobasilar system. In a complete subclavian steal, the arterial supply to the arm is via blood flowing exclusively in a retrograde direction down the vertebral artery at the expense of the vertebrobasilar circulation. In an incomplete steal, vertebral artery flow may be biphasic, or flow reversal may be induced by exercise.2 Doppler findings of a subclavian steal have been extensively described.2,3 However, to our knowledge, a sub-
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clavian steal following intentional occlusion of the left subclavian artery has not been described in the ultrasound literature, nor have the Doppler findings of this common iatrogenic cause been illustrated. When the left subclavian artery origin is covered during thoracic endovascular aortic repair, circulation to the arm and vertebrobasilar system can be maintained by revascularization, typically either by transposition of the left subclavian artery to the left carotid or by a left carotid-to-left subclavian artery bypass. The need for revascularization is controversial and has been the subject of numerous vascular surgery studies.4–10 We observed the following sonographic findings in a patient who underwent thoracic endovascular aortic repair with intentional occlusion of the left subclavian artery. A 30-year-old man was brought to our center after a motorcycle collision and fall of approximately 100 ft. Initial imaging showed multiorgan system trauma, including traumatic aortic injury with a pseudoaneurysm of the distal aortic arch. He also had hepatic and splenic lacerations, extremity and pelvic fractures, and intracranial hemorrhage. The patient underwent exploratory laparotomy with packing of the abdomen for active bleeding of the liver. Two days after admission, the vascular surgery service performed thoracic endovascular aortic repair, with intentional occlusion of the left subclavian artery due to the location of the pseudoaneurysm. He also underwent reduction of multiple extremity fractures, with the exception of a left distal radius fracture. Minimal antegrade flow was seen in the occluded left subclavian artery on angiography immediately after thoracic endovascular aortic repair (Figure 1A). One week after aortic repair, the patient underwent a carotid duplex study as part of routine follow-up. The study showed flow reversal in the left vertebral artery, consistent with a complete subclavian steal (Figure 1B). The left subclavian artery was also abnormal, showing a monophasic, low-resistance waveform (Figure 1C). The right subclavian artery showed a normal triphasic waveform and highresistance flow. The patient’s mental status was still altered at this time, and although symptoms of the subclavian steal could not be accurately assessed, spontaneous left upper extremity movements were noted. Due to both the subclavian steal documented on sonography and the concomitant left radius fracture, the patient was taken for an uncomplicated left subclavian artery-to-left carotid artery transposition. Carotid duplex sonography 2 weeks later showed biphasic waveforms in the left vertebral artery (Figure 1D), as opposed to complete vertebral artery reversal preoperatively. This duplex study also showed normal high-
J Ultrasound Med 2015; 34:925–929
resistance systolic waveforms in the left subclavian artery, as opposed to low-resistance waveforms preoperatively. The findings were consistent with conversion of a complete subclavian steal to an incomplete steal after revascularization. The patient was extubated, with improving mental status soon after. Several early and smaller studies in the vascular surgery literature described good outcomes following left subclavian artery occlusion without prophylactic revascularization. Hausegger et al4 described 4 patients who required left subclavian artery occlusion during thoracic endovascular aortic repair. Although no neurologic complications or left arm ischemia were observed, the authors did note that left arm systolic blood pressures were lower than those of the right arm. Görich et al5 described 23 patients who required left subclavian artery coverage during thoracic endovascular aortic repair. Symptoms of left arm ischemia were described in 2 patients (exercise-related left hand paresthesias and a cool left hand). However, both patients refused revascularization due to spontaneous symptomatic improvement. The authors concluded that left subclavian artery coverage is generally well tolerated. Rehders et al6 reported 22 patients who required complete coverage of the left subclavian artery during thoracic endovascular aortic repair. There were no serious morbidities at a mean 2-year follow-up, although the mean differential systolic blood pressure in the left arm was 26% lower than in the right arm. Mild symptoms of a subclavian steal in 7 patients included exercise-induced weakness in 3, a mild sensation of left arm coolness in 3, and left arm paresthesias in 1. The authors challenged the need for prophylactic revascularization. Numerous other studies have reported higher complication rates for left subclavian artery occlusion without revascularization. Tiesenhausen et al7 performed thoracic endovascular aortic repair necessitating left subclavian artery occlusion in 10 patients, the first 2 of whom underwent prophylactic left subclavian artery-to-left carotid artery transposition. The remaining 8 patients were managed expectantly. Three of these 8 patients required left subclavian artery revascularization for subclavian steal syndrome with vertigo and left arm claudication. The authors concluded that prophylactic revascularization should be performed in patients with severe disease of the vertebral or internal carotid arteries. Riesenman et al8 performed thoracic endovascular aortic repair on 112 patients, a subset requiring complete (18 patients) or partial (10 patients) left subclavian artery coverage. Subclavian steal symptoms developed in 3 patients
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with complete left subclavian artery coverage, but none had symptoms severe enough to warrant intervention. Left arm rest pain developed in 1 patient with partial left subclavian artery coverage and was successfully treated by deployment of a left subclavian artery stent.
Figure 1. Complete subclavian steal following left subclavian artery occlusion during thoracic endovascular aortic repair, converted to an incomplete steal following left subclavian artery revascularization. A, Thoracic endovascular aortic stent-graft occluding the origin of the left subclavian artery (arrow). Blood flow in the thoracic aorta around the graft, often seen just after stent placement, is responsible for the minimal residual flow in the left subclavian artery. B, Initial Doppler examination showing reversal of flow in the left vertebral artery, consistent with a complete subclavian steal after left subclavian artery occlusion by a stent-graft. C, Initial Doppler examination showing an abnormal lowvelocity, low-resistance, monophasic waveform in the left subclavian artery after occlusion by the stent-graft. The left subclavian artery waveform normalized after revascularization (not shown). D, Doppler examination following revascularization (left subclavian artery-to-left carotid artery transposition) showing a biphasic left vertebral artery waveform, now consistent with an incomplete subclavian steal.
B
C
A
D
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In recent years, several meta-analyses and reviews have also examined the need for prophylactic revascularization of the left subclavian artery before occlusion. Rizvi et al9 compiled a meta-analysis of 51 observational studies and concluded that very low-quality evidence suggests that left subclavian artery coverage increases the risk of arm ischemia, vertebrobasilar ischemia, and possibly spinal cord ischemia and anterior circulation stroke. There were no significant associations between left subclavian artery coverage and death, myocardial infarction, or transient ischemic attacks. A review by Weigang et al10 concluded that only in acutely unstable patients is left subclavian artery coverage without prophylactic revascularization justified. Prophylactic revascularization of the left subclavian artery before coverage was deemed necessary in the setting of a dominant left vertebral artery, anomalous subclavian or vertebral arteries (such as a direct aortic arch origin of the left vertebral), functional compromise of the posterior circulation, and a prior coronary artery bypass graft using the left internal mammary artery. Left subclavian artery coverage without revascularization in any of these conditions could compromise the left arm or posterior circulation collateral blood supply. To our knowledge, the Doppler findings of a complete subclavian steal resulting from intentional left subclavian artery occlusion during thoracic endovascular aortic repair have not been reported previously. We also document improvement in the steal phenomenon, with conversion to an incomplete steal (biphasic waveforms) in the left vertebral artery after revascularization. With the increasing use of thoracic endovascular aortic repair with left subclavian artery occlusion for treatment of thoracic aortic disorders, this iatrogenic etiology of a subclavian steal may be observed more frequently in the future. Practitioners performing cerebrovascular sonography should be aware of this phenomenon. Doppler evaluation can play a part in preoperative evaluation of the carotid and vertebral circulation to identify candidates for prophylactic revascularization. In patients undergoing emergent thoracic endovascular aortic repair with left subclavian artery occlusion, preoperative Doppler imaging or revascularization may not be feasible. In these cases, Doppler documentation of the presence and severity (complete versus incomplete) of a subclavian steal following thoracic endovascular aortic repair may contribute to the decision to revascularize the left subclavian artery.
doi:10.7863/ultra.34.5.926
References 1.
Hausegger KA, Oberwalder P, Tiesenhausen K, et al. Intentional left subclavian artery occlusion by thoracic aortic stent-grafts without surgical transposition. J Endovasc Ther 2001; 8:472–476. 2. icenzini E, Ricciardi MC, Sirimarco G, Di Piero V, Lenzi GL. Extracranial and intracranial sonographic findings in vertebral artery diseases. J Ultrasound Med 2010; 29:1811–1823. 3. Ginat DT, Bhatt S, Sidhu R, Dogra V. Carotid and vertebral artery Doppler ultrasound waveforms: a pictorial review. Ultrasound Q 2011; 27:81–85. 4. Hausegger KA, Tiesenhausen K, Schedlbauer P, Oberwalder P, Tauss J, Rigler B. Treatment of acute aortic type B dissection with stent-grafts. Cardiovasc Intervent Radiol 2001; 24:306–312. 5. Görich J, Asquan Y, Seifarth H, et al. Initial experience with intentional stent-graft coverage of the subclavian artery during endovascular thoracic aortic repairs. J Endovasc Ther 2002; 9(suppl 2):II39–II43. 6. Rehders TC, Petzsch M, Ince H, et al. Intentional occlusion of the left subclavian artery during stent-graft implantation in the thoracic aorta: risk and relevance. J Endovasc Ther 2004; 11:659–666. 7. Tiesenhausen K, Hausegger KA, Oberwalder P, et al. Left subclavian artery management in endovascular repair of thoracic aortic aneurysms and aortic dissections. J Card Surg 2003; 18:429–435. 8. Riesenman PJ, Farber MA, Mendes RR, Marston WA, Fulton JJ, Keagy BA. Coverage of the left subclavian artery during thoracic endovascular aortic repair. J Vasc Surg 2007; 45:90–95. 9. Rizvi AZ, Murad MH, Fairman RM, Erwin PJ, Montori VM. The effect of left subclavian artery coverage on morbidity and mortality in patients undergoing endovascular thoracic aortic interventions: a systematic review and meta-analysis. J Vasc Surg 2009; 50:1159–1169. 10. Weigang E, Parker JA, Czerny M, et al. Should intentional endovascular stent-graft coverage of the left subclavian artery be preceded by prophylactic revascularisation? Eur J Cardiothorac Surg 2011; 40:858–868.
Mittul Gulati, MD, Nasim Khadem, MD, Ilya Lekht, MD, Hisham Tchelepi, MD, Edward G. Grant, MD Department of Radiology University of Southern California Keck School of Medicine Los Angeles, California USA J Ultrasound Med 2015; 34:925–929
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